I am begining to wonder if my fan clutch is bad. I have a slight overheating issue that is only noticeable when the blazer is in 'city' conditions. If I am on the highway for a long period of time and then exit to stop signs and lights it begins to overheat. Along with the overheating, when I begin to apply gas it starts sounding like an airplane getting ready to take off. Itll roar for a few seconds and then quiet down.

Also I am able to turn the hand fairly freely after a couple of turns and from what I understand that could be a possible indication that my clutch has gone bad.

I think I have narrowed it down to it being a clog in the radiator or the fan clutch but wanted some other perspective.

Those are the symptoms of a bad fan clutch. OE clutch is an AC Delco 15-4684 thermostatic control, reverse rotation, with A.C. Those are expensive but they will last 20 years. If you are going to get rid of the vehicle in a year or two, get a cheap Hayden fan clutch.

Both clutches will do the job but the AC Delco fan clutch will last longer.

Sounds like the fan clutch is working correctly, the roar you hear is the clutch locking up and then unlocking once the air cools down. The clutch only works at slower speeds, once you hit about 20 mph(depending on ambient temp) the air is just moving too fast thru the radiator to pick up enough heat to keep the fan clutch engaged. you should be able to move the clutch freely unless you just turned the truck off while the clutch is engaged and you tried to turn the fan is a few seconds after.

Sound more like your just not getting enough coolant movement at idle, which is most likely a water pump. Let the truck idle till it starts to run hot and the clutch kicks on then rev and hold at 1000-1500 rpm for about 30 seconds and see if the temp drops

Also my water pump was recently replaced (about three weeks ago) along with upper and lower hoses. Thermostat was replaced last summer when I was having this issue. This weekend I was looking at doing a coolant flush. I have checked inbetween the rad and condensor and there isnt any kind of debris. I have not yet checked the radiator for any cool spots.

I know my heater core needs to be flushed as I get no heat in the cab, but I also do know that has nothing to do with the circulation of the coolant and wouldnt cause the overheating.

My 99 blazer would run around 215-220 + in the sumer with a/c on. the heater core was clogged. I cleaned out the heater core and it now runs less than 200 with a/c on idling for hours. It has been close to 90 degrees lately. no issues as of yet.

I need to do a core flush. Unfortunately it is raining ATM and I dont like working in the rain.

Hopefully tomorrow will provide me with the opportunity.

I also have noticed on occasion, usually after a cold start that there is some gurgling coming from the heater core area. Is that air in the system? If so how do I get it out. I dont think I have found a successful way to flush that air out

The "roar" you hear is an indication the fan clutch is NOT working properly. The fan clutch thermostatic bi-metal spring should allow the fan to freewheel until the engine overheats. If the fan clutch is good, you will never hear the fan.

I am just a bit confused. I thought the "roar" was an indication that the fan clutch was working properlly? Meaning that it was engaging and that the extra sound is the air its pulling in/pushing through the engine compartment. Am I understanding it incorrectly?

The clutch should never lock up completely. If the fan clutch locks up completely, the clutch is stuck and you will hear the fan like an airplane propeller. That indicates the the fan clutch is defective. When the fan clutch sticks and engages solid or if it never engages, it is defective.

A defective fan clutch may engage at high speed and block the incoming air flow through the radiator and the engine will overheat, or it can disengage at idle and not pull sufficient air through the radiator and the engine will overheat. When either happens, it means the fan clutch is defective.

Replaced mine recently. They should not move freely but have some good resistance. Roars when first started up for a minute but goes away when you drive for a minute. Same if i were sitting at a stop light. Normal.

When you say they should not move freely, is that both in hot and cold states?

Earlier while my engine was still warm I attempted to move the fan and it would stop almost as soon as I removed my hand. I have tested it before while it was cold and I have been able to make it rotate a few times without much resistance.

you should do the "free spin test" while the engine is at operating temp. ideally it should stop spinning almost immediately after you stop spinning it, and it shouldn’t spin more than half a full rotation after you try spinning it.

It sounds like your fan is doing its job when theres not enough air flow. Look into getting that dexcool out by flushing your system very well and replace with green 50/50 antifreeze. May wanna check and replace t stat if needed. Radiators can clog too.

Vinegar is a mild acid but not acidic enough to do any good. I thought about using phosphoric acid diluted with distilled water but decided not to try it. Acid chemicals should not be used as a radiator flush because it can react and emulsify with other minerals in the system.

Avoid home remedies and get Prestone Radiator flush and a flush kit and follow the instructions. Always use Prestone Pre-Mixed Long life coolant and top the radiator off with distilled water if necessary. . Always use distilled water any time you must add water to the radiator, battery or the windshield washer tank.

Use 100% distilled water in your windshield washer tank in summer and windshield 10 degree washer antifreeze fluid in winter, but only if you live in a cold climate. Never use a colder rated washer fluid and do not use windshield fluid any longer than you have to and only long enough to prevent the washer system from freezing. The antifreeze element in windshield washer fluid is alcohol and alcohol will ruin the plastic parts and the windshield washer spray nipples. Occasionally run the windshield washer using distilled water to flush the system.

A thermostatic variable fan clutch should not begin to engage when the engine is cool. If it does, the fan clutch is defective. A thermostatic fan clutch will slowly engage at idle and low speed when the engine is overheating and slowly disengage at high speed when the fan is not needed to pull air through the radiator. The fan clutch will not "lock up" suddenly and if it does, the fan clutch is defective.

A good fan clutch will slowly engage and slowly disengage according to the ambient temperature and you should not hear any fan noise. If you hear fan noise, the thermostatically controlled fan clutch is defective and is not functioning properly.

A fan clutch is defective it if the fan free wheels or if it locks up. A test of a fan to determine if it is freewheeling or locked up is to roll up one sheet of newspaper and stick it into the fan with the engine cool and idling. If the newspaper roll prevents the fan from turning, the fan clutch is defective. If the fan shreds the newspaper, the fan clutch is locked up and it is defective.

A thermostatic variable fan clutch should not begin to engage when the engine is cool. If it does, the fan clutch is defective. A thermostatic fan clutch will slowly engage at idle and low speed when the engine is overheating and slowly disengage at high speed when the fan is not needed to pull air through the radiator. The fan clutch will not "lock up" suddenly and if it does, the fan clutch is defective.

A good fan clutch will slowly engage and slowly disengage according to the ambient temperature and you should not hear any fan noise. If you hear fan noise, the thermostatically controlled fan clutch is defective and is not functioning properly.

A fan clutch is defective it if the fan free wheels or if it locks up. A test of a fan to determine if it is freewheeling or locked up is to roll up one sheet of newspaper and stick it into the fan with the engine cool and idling. If the newspaper roll prevents the fan from turning, the fan clutch is defective. If the fan shreds the newspaper, the fan clutch is locked up and it is defective.

I had to replace mine a few months ago because it completely locked up. The replacement engages in the mornings till I drive a couple hundred feet and the "roar" goes away. When I get off work and the truck has been sitting in the hot sun... I do not hear the fan. I thought since it disengages at a certain RPM and stays disengaged that it means the clutch was working at least partially but I never felt comfortable that it was working correctly. Why couldn't these trucks have come with electric fans?? GM was putting electric fans in cars in the early 90's and possibly earlier... my truck is an 03!

I used to have an old mechanic that worked at my dealership that used to say the best thing for a coolant flush was citric acid. Yes oj, not in the fruit form though. Said citric acid was really good at breaking down scale and rust without causing damage or pitting in metals.

I had to replace mine a few months ago because it completely locked up. The replacement engages in the mornings till I drive a couple hundred feet and the "roar" goes away. When I get off work and the truck has been sitting in the hot sun... I do not hear the fan. I thought since it disengages at a certain RPM and stays disengaged that it means the clutch was working at least partially but I never felt comfortable that it was working correctly. Why couldn't these trucks have come with electric fans?? GM was putting electric fans in cars in the early 90's and possibly earlier... my truck is an 03!

Did you install a thermostatically controlled viscous clutch or a plain viscous clutch?

The original equipment GM / AC Delco or Dorman reproduction fan clutch is thermostatically controlled and they can cost as much at $80 - $250 msrp. The GM or Dorman repro fan clutch will have a external bi-metal spring attached to the center shaft. The bi-metal spring controls the main shaft and the internal valving. The modern cars since the mid to late 1990s cannot use a thermostatically controlled fan clutch because they do not have enough room for a large radiator, a thermostatically controlled fan clutch and the fan shrouds. If the passenger cars and street rods today had enough room under the hood, they would not be using electric fans.

The cheap viscous fan clutches such as Hayden or Flex-A-Lite can be purchased for $35 - $40 at any independent auto parts store and are ineffective after 10,000 - 20,00o miles but they will get a customer "out the door". The cheap viscous fan clutch is centrifugally controlled by the engine RPM and not by the ambient temperature.

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